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Discussion Starter · #1 ·
Hi Everyone

The Battery gave up and had to improvise opening the frunk with a second discharged Mercedes AMG donor Battery which I had to charging it via an inventor through standard charger,

ANYWAY!

After took the dead battery out noticed the Mercedes Battery is AGM and the dead 987.2 Cayman battery is Costco Kirkland Non AGM which previous owner changed it, both had similar size and specification so I gave it a try put the Mercedes half-charged battery in and it cranked started like a brand new car!

did a bit of research and lots of stories.

my Question is :
If the AGM battery stays in the car will it damage the alternator or charging system, I know AGM and Non AGM has different charge pattern.
Car is 2009 Cayman S PDK if matters

Cheers
P.S: Apologies if this has been asked before Newbie here in the site
 

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I have been told by the "experts" who answer questions for the Porsche Club of America that the two types of batteries are interchangeable with no negative impact. I currently have a Lead Acid wet cell battery in my 2008 Cayman and will be going with the AGM at replacement time based on the just mentioned advice.
 

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AFAIK they're completely interchangeable and using an AGM definitely won't damage the car. In my experience AGM batteries like a bit higher charging voltage and are less tolerant of deep discharge, but that's generally not an issue when using them on modern cars with good charging systems.

The main advantage of AGM batteries is that they're less likely to leak, which will make a mess and damage things. Note that the Cayman has a battery drain line you should definitely hook up, especially if you use a standard battery (AGM batteries generally have a place to connect it but it shouldn't ever do anything on an AGM battery unless something goes seriously wrong, in my understanding).
 

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I believe where the difference lies in your old faithful battery maintainer, that has to be replaced for a float charger with an AGM setting
I have a couple 3 amp types from Schumacher, one about 5 years old and one about 1 year old. The 5 year old version says it's for lead acid/AGM batteries (either type), and the newer one says it's for lead acid/AGM, or lithium, with a button push depending on type. So I'm covered. I suspect a maintainer upgrade may dependent on the amp rating but not certain.
 

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Discussion Starter · #6 · (Edited)
Finally I called someone at dealership part section, they told me the original battery was Non-AGM which few years ago Porsche has rolled out AGM for all of these cars and fully compatible with charging system, he even sent me a quotation if I want to buy one of those 9A7-915-105-A $370CAD which is not too bad for OEM, the Mercedes cost me $450).

but since this Mercedes-AMG AGM battery is working smooth and cranking up the engine like modern new engines I'm gonna let it sit in Cayman for few days and then order a new one from Porsche. that's the battery I replaced for Mercedes because Stop/start was not engaging and was sitting in the storage for about 5 months.

some photos of these batteries, so I moved from with Costco Kirkland 80AH Non AGM ==> Mercedes 80AH AGM ,,,, I hope nothing breaks. :D

Thanks for reminder, I connected the Vent!
 

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The main advantage of AGM batteries is that they're less likely to leak, which will make a mess and damage things. Note that the Cayman has a battery drain line you should definitely hook up, especially if you use a standard battery (AGM batteries generally have a place to connect it but it shouldn't ever do anything on an AGM battery unless something goes seriously wrong, in my understanding).
That's actually a VENT line, and it is important to connect it no matter what sort of battery you're installing. The flooded-lead battery gives off acid vapors - the vent takes them outside of the frunk area where otherwise they'd cause major corrosion. AGM batteries - if overcharged give off hydrogen sulfide. Florida officials say driver and daughter inhaled poison gas and died

You really don't want that in the trunk either. Consider where the HVAC air inlet is..
 
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